1. Field of the Invention
The present invention relates to wireless networks; more particularly, the optimization of wireless networks.
2. Description of the Related Art
When wireless networks such as cellular or PCS Personal Communication Services) networks are installed, their initial operating parameters are based on models that attempt to describe the physical environment in which the network will be operating. The operating parameters control characteristics such as signal transmit power and handoffs between cells. The model is provided with the available, but often incomplete, topographical information such as the location and size of hills or buildings that may block signal propagation. Using the model and available topographical and demographic data, network planning tools are used to predict the performance of the network, particularly, at "hot spots" where there is a large demand for network resources. Unfortunately, the model and topographical information used in the network planning is often inaccurate. In order to compensate for these inaccuracies, the wireless network is tuned after installation by adjusting the operating parameters to try to provide signal coverage to delivered areas and to provide sufficient network resources to hot spots. This process is typically referred to as optimization. The parameters include antenna height and tilt which control the footprint or area that will receive transmissions from the antenna Transmission power is also adjusted to vary cell size and to minimize interference caused by different transmitters or base stations within the network. Neighbor lists are adjusted so that a mobile in contact with a particular transmitter or base station, will know which other base stations are most likely to provide a successful handoff when it moves away from its present base station.
FIG. 1 illustrates a portion of a wireless network. Base stations 10, 12, 14, 16, 18, 20, and 22 each transmit signals to, and receive signals from, mobile units within the coverage area of each base station. The coverage area is indicated by the hexagon surrounding each of the base stations. The hexagons are a convenient representation for the coverage area of each base station; however, in the real world the shape is other than hexagonal due in part to the characteristics of the area surrounding the base station. Additionally, the location of the transmitter may not be in the center as shown in FIG. 1. The base stations are in communication with mobile switching center (MSC) 30. MSC 30 connects each base station to other communication networks such as the public switched telephone network or other MSCs of the same network and provides each base station with access to data bases that are used for tasks such as verifying the identity of a mobile unit before it is allowed to use the wireless network. As discussed above, the wireless network should be optimized to provide most areas with acceptable receive signals transmitted by the base station(s). In order to ensure that all areas receive signals from their respective base stations, route 40 is determined and is then driven by a vehicle carrying test equipment. Route 40 is chosen to pass through selected areas where signal reception may be weak or non-existent due to, for example, hills or buildings. Route 40 is also chosen to go through areas where user demand for network resources will be particularly heavy and areas that are important due to other reasons. As the vehicle carrying test equipment is driven along route 40, the wireless network performance is monitored. Test equipment records the vehicle's position, the signal strength received from base stations in the area, bit error rate, frame error rate, signal to interference ratio and dropped call information. By measuring base station signal strength, it can be determined whether signal strength for a particular base station should be increased or decreased, or whether the antenna associated with that base station should be adjusted to provide more uniform signal coverage. Additionally, by measuring the base station signal strength of several base stations, the neighbor list provided to the mobile units can be updated to include only the base stations that provide the best signals for that location.
Once the vehicle has driven the route and collected the test data, the data is brought to a processing center where the data is analyzed and new parameters are determined for the base stations. These parameters are then used to adjust the operation of each of the base stations. Once the base stations have been modified to operate with the new parameters, the test vehicle is once again driven along route 40 and data measurements are taken. These measurements are then once again brought back to the processing center where they are analyzed to provide new parameters for the base stations. The base stations are then modified in accordance with the parameters and once again the test vehicle drives route 40 to collect new data. This process is repeated many times until satisfactory performance is measured along route 40. This process is illustrated in FIG. 2.
FIG. 2 illustrates the steps described above in optimizing the wireless network. Step 60 involves selecting a cluster or group of cells as illustrated in FIG. 1 for testing. Step 62 involves determining route 40 in order to test performance within the cluster. Step 64 involves driving along route 40 to record data and step 66 involves processing the data at a processing center to determine system performance. Step 68 involves plotting a map that shows system performance relative to location along route 40. In step 70 it is determined whether the target performance has been reached. If the target performance has not been reached, step 72 is executed where problems are identified and new base station parameters are determined. Step 74 is then used to tune the base stations in accordance with the parameters determined in step 72. After step 74, the process is repeated starting with step 64 where route 40 is driven to collect test data. If at step 70, it is determined that the target performance has been reached, step 78 is executed where it is determined whether all the cluster of cells for the network system have been tested. If all the clusters have not been tested, step 60 is executed where a new cluster is selected for testing. If all the upper clusters have been tested, step 80 is executed where a global test of the network is conducted. This test involves monitoring of voice quality and verifying that the handoffs occur where expected. In step 82 it is determined whether target performance for the wireless network has been achieved. If the target has been achieved, the process ends until an update or other changes are required. If the target performance has not been reached, the process returns to step 60 where a cluster is selected to begin the testing and optimization of the system once again.
The above-described method for optimizing a wireless network is slow and costly. A vehicle must repeatedly be driven over a test route in order to collect data that is used to evaluate and then improve the network performance. Also, the trial and error approach underlying this method makes it very difficult to reach optimal performance leaving networks with less than optimal performance. Repeatedly driving this route requires a great deal of time and keeps an expensive wireless network from generating significant revenue for periods of time that may last up to several weeks.